Bryan Hartnell had originally told the park ranger (shortly after the attack) that Zodiac claimed to have escaped from a prison in Colorado. The following day, he told detectives that it was a prison in Montana. Police decided, for some reason, to go with "Deer Lodge Prison" in Montana. This is fishy. Hartnell was pretty doped up once he was in the hospital, so I think it's more probable that Zodiac said Colorado and not Montana, although there is no way of knowing for sure.

Most Zodiac researchers have studied Deer Lodge and other Montana prisons. Hatrnell said that the name of the prison sounded like "fern lock," or something along those lines. Here is a list of Colorado prisons/correctional institutions that I have found. I'm not sure which of these were around back then, but none of them sound close to "fern lock."